1. Field of the Invention
The present invention most directly relates to alignment of two or more directional devices, and more particularly, to alignment of sighting devices. The invention further relates specifically to dynamically aligning sighting devices to allow two or more users to easily locate a common target object through independently translated viewing ports.
2. Description of the Prior Art
Sighting devices, particularly optical sighting devices, are used in many applications and are varied in configuration. Common optical sighting devices include, but are by no means limited to, binoculars, telescopes, rifle and other weapon sights, and surveying equipment. A user might sight through an optical device, generally, to (a) magnify or otherwise improve viewing of a target in the visual field and/or (b) to align an attached piece of equipment (e.g., rifle, survey tool, etc.) with a target.
In certain sighting applications, situations arise in which two or more users working together need to share information about target location so that both may view the same scene. For example, a bird watcher may wish to convey the location of a bird to a second bird watcher so that they both can focus quickly on the same bird. As a further example, one party equipped with a wide field optical device may wish to guide a second party equipped with a high power, narrow field optical sight towards a target object. Sighting applications in which it is desirable to share information between users also include tree and geologic identification, ship and terrain spotting at sea, aircraft spotting and identification, and military targeting, such as when a spotter with one optical device guides a second person equipped with an optically sighted weapon towards a specified target.
Communication between sighting device users is often in the form of haphazard directional descriptions, such as, “Two o'clock, a few degrees above the horizon,” or, “A little below the top branch of the tall forked tree.” Previous solutions to this shortcoming have included providing internal compass and declinometer readings in the displays of prior art sighting devices. Through such a display, users may communicate direction using precise numbers to co-ordinate their targeting. Other devices of the prior art have implemented detection of rotation via gyroscopically stabilized platforms, thereby subsequently conveying directional information to a remote user. This latter method, however, requires an initial coordinate alignment step to synchronize the two devices, which may preclude certain spontaneous operations.
An effort to overcome some of the shortcomings addressed above, while demonstrating other shortcomings, is disclosed in U.S. Pat. No. 5,764,344 issued to Taniguchi. The reference discloses an observing apparatus for simultaneous viewing of an object by two different users. A first operator locates a target through a first telescope and depresses a detection switch when the target is adequately framed in his field of view. An arithmetic control unit, upon notification that the detection switch has been activated, determines the distance from the first telescope to the target as well as a set of coordinates of the target. The coordinates are subsequently transmitted over a cable to a second telescope under the control of a second operator. At the second telescope, an arithmetic control unit activates indicators in the viewing field of the second operator, which specify to the second operator a direction of rotation through which the second telescope must be rotated in order for the target to be framed in the field of view of the second telescope.
While the visual feedback provided to the second operator directing her towards the location of the target ameliorates verbal direction commands such as those discussed above, several deficiencies of the Taniguchi system limit its range of applicability. First, the referenced system utilizes an absolute frame of reference, i.e., both telescopes are configured, via rotational encoders, to locate a point in a previously established coordinate system. Establishing the coordinate system is an involved process, as disclosed in the reference, involving calibrating both telescope platforms on a previously designated calibration target. Ironically, both operators must locate the same calibration target in their respective fields of view, which is the target location problem alleviated by the present invention. The Taniguchi system, though, first requires that the telescopes be collocated for a first calibration measurement prior to moving the second telescope to a remote location, where the second operator must once again locate the calibration target and make a second calibration measurement. The two telescopes then remain fixed in their respective locations for the duration of ordinary viewing operations, as the invention does not provide a means to dynamically recalibrate if one or the other user relocates.
A further shortcoming of the Taniguchi system lies in its means for determining the absolute bearing in the chosen coordinate system. The embodiments disclosed by the reference utilize rotational encoders on respective, fixed tripods of equal length. The tripod serves to fix the telescopes within the coordinate system and provides a non-rotating reference base for the rotational encoders. It should be apparent to the skilled observer that such a system severely restricts the movement of its users.
However, rotational encoders are not the only means by which absolute bearing may be determined. Other bearing sensors include magnetic compasses, which are known to be affected indeterminately by local magnetic disturbances, such as metal objects and electronic equipment. Rotational accelerometers are also capable of providing an absolute bearing, but are subject to drift. Neither of these devices can provide consistent reliable accuracy for aligning optical systems having magnification.
Certain military and camera devices utilize an instrument or weapon that is slaved to automatically move in response to adjustments in a remote optical sight. The mechanically slaved techniques of the prior art often rely on fixed spatial relationships and pre-alignment to solve the problem of common targeting. While duplicating, or even translating, the movement of one device through pointing movements of another device is both well-known and useful, the technique can be limiting in other sighting applications. For example, in certain applications, users should be allowed to aim their respective sighting equipment freely and independently of the aim of other sighting devices, until such time as one user wishes to direct another to view a common target object. At that time, communicating alignment information between users is warranted. Even then, a user may wish to ignore the sightings of other users and continue aiming his own equipment independently, a option that would not be possible in systems practicing the mechanical slaving techniques of the prior art.
In light of the shortcomings of the prior art, there is an apparent need for sighting devices that are operable to communicate alignment between two or more passively aimed devices.